Oil, gas, water, geothermal wells and the like are typically drilled with a drill bit connected to a hollow drill string which is inserted into a well casing cemented in a well bore. A drilling head is attached to the well casing, wellhead or to associated blowout preventor equipment, for the purposes of sealing the interior of the well bore from the surface and facilitating forced circulation of drilling fluid through the well while drilling or diverting drilling fluids away from the well. Drilling fluids include, but are not limited to, water, steam, drilling muds, air, and other fluids (i.e., liquids, gases, etc).
In the forward circulation drilling technique, drilling fluid is pumped downwardly through the bore of the hollow drill string, out the bottom of the hollow drill string and then upwardly through the annulus defined by the drill string and the interior of the well casing, or well bore, and subsequently out through a side outlet above the well head. In reverse circulation, a pump impels drilling fluid through a port, down the annulus between the drill string and the well casing, or well bore, and then upwardly through the bore of the hollow drill string and out of the well.
Drilling heads typically include a stationary body, often referred to as a bowl, which carries a rotatable spindle, which is commonly referred to as a bearing assembly, rotated by a kelly apparatus or top drive unit. One or more seals or packing elements, often referred to as stripper packers or stripper rubber assemblies, is carried by the spindle to seal the periphery of the kelly or the drive tube or sections of the drill pipe, whichever may be passing through the spindle and the stripper rubber assembly, and thus confine or divert the core pressure in the well to prevent the drilling fluid from escaping between the rotating spindle and the drilling string.
As modern wells are drilled ever deeper, or into certain geological formations, very high temperatures and pressures may be encountered at the drilling head. These rigorous drilling conditions pose increased risks to rig personnel from accidental scalding, burns or contamination by steam, hot water and hot, caustic well fluids. There is a danger of serious injury to rig workers when heavy tools are used to connect a stripper rubber assembly to the drilling head. Accordingly, such a connection should be made quickly and achieve a fluid tight seal.
Rotation of respective rotating components of a rotating control head, rotating blowout preventor or other type of rotating control device is facilitated through a bearing assembly through which the drill string rotates relative to the stationary bowl or housing in which the bearing assembly is seated. Rotating control heads, rotating blowout preventors and other types of rotating control devices are generally referred to herein as well drilling heads. Typically, a rubber O-ring seal, or similar seal, is disposed between the stripper rubber assembly and the bearing assembly to improve the fluid-tight connection between the stripper rubber assembly and the bearing assembly. Pressure control is achieved by means of one or more stripper rubber assemblies connected to the bearing assembly and compressively engaged around the drill string. At least one stripper rubber assembly rotates with the drill string. A body of a stripper rubber assembly (i.e., a stripper rubber body) typically taper downward and include rubber or other resilient substrate so that the downhole pressure pushes up on the stripper rubber body, pressing the stripper rubber body against the drill string to achieve a fluid-tight seal. Stripper rubber assemblies often further include a metal insert that provide support for bolts or other attachment means and which also provide a support structure to minimize deformation of the rubber cause by down hole pressure forces acting on the stripper rubber body.
Stripper rubber assemblies are connected or adapted to equipment of the drilling head to establish and maintain a pressure control seal around the drill string (i.e., a down hole tubular). It will be understood by those skilled in the art that a variety of means are used to attach a stripper rubber assembly to associated drilling head equipment. Such attachment means include bolting from the top, bolting from the bottom, screwing the stripper rubber assembly directly onto the equipment via cooperating threaded portions on the top of the stripper rubber assembly and the bottom of the equipment, clamps and other approaches.
It will be understood that, depending on the particular equipment being used at a drilling head, a stripper rubber assembly at one well may be connected to equipment specific to that well while at another well a stripper rubber assembly is connected to different equipment. For example, at one well the stripper rubber assembly may be connected to the bearing assembly while at another well the stripper rubber assembly may be connected to an inner barrel or an accessory of the drilling head. Thus, the stripper rubber assembly is not unnecessarily limited to being connected to a particular component of a rotating control head, rotating blowout preventor or the like.
It is common practice to tighten the bolts or screws of the connection with heavy wrenches and sledge hammers. The practice of using heavy tools to tighten a bolt, for example, can result in over-tightening, to the point where the threads or the bolt head become stripped. The results of over-tightening include stripped heads, where the bolt or screw cannot be removed, or stripped threads, where the bolt or screw has no grip and the connection fails. Both results are undesirable. Even worse, vibration and other drilling stresses can cause bolts or screws to work themselves loose and fall out. If one or more falls downhole, the result can be catastrophic. The drill bit can be ruined. The entire drillstring may have to tripped out, and substantial portions replaced, including the drill bit. If the well bore has been cased, the casing may be damaged and have to be repaired.
Drilling head assemblies periodically need to be disassembled to replace stripper rubber assemblies or other parts, lubricate moving elements and perform other recommended maintenance. In some circumstances, stripped or over tightened bolts or screws make it very difficult if not impossible to disengage the stripper rubber assembly from the drilling head assembly to perform recommended maintenance or parts replacement.
One prior art rotating control head configuration that is widely used rotating control heads in the oil field industry is the subject of U.S. Pat. No. 5,662,181 to John R. Williams (i.e., the Williams '181 patent). The Williams '181 patent relates to drilling heads and blowout preventors for oil and gas wells and more particularly, to a rotating blowout preventor mounted on the wellhead or on primary blowout preventors bolted to the wellhead, to pressure-seal the interior of the well casing and permit forced circulation of drilling fluid through the well during drilling operations. The rotating blowout preventor of the Williams '181 patent includes a housing which is designed to receive a blowout preventor bearing assembly and a hydraulic cylinder-operated clamp mechanism for removably securing the bearing assembly in the housing and providing ready access to the components of the bearing assembly and dual stripper rubber assemblies provided in the bearing assembly. A conventional drilling string is inserted or “stabbed” through the blowout preventor bearing assembly, including the two base stripper rubber assemblies rotatably mounted in the blowout preventor bearing assembly, to seal the drilling string. The device is designed such that chilled water and/or antifreeze may be circulated through a top pressure seal packing box in the blowout preventor bearing assembly and lubricant is introduced into the top pressure seal packing box for lubricating top and bottom pressure seals, as well as stacked radial and thrust bearings.
Primary features of the rotating blowout preventor of the Williams '181 patent include the circulation of chilled water and/or antifreeze into the top seal packing box and using a hydraulically-operated clamp to secure the blowout preventor bearing assembly in the stationary housing, to both cool the pressure seals and provide access to the spaced rotating stripper rubber assemblies and internal bearing assembly components, respectively. The clamp can be utilized to facilitate rapid assembly and disassembly of the rotating blowout preventor. Another primary feature is mounting of the dual stripper rubber assemblies in the blowout preventor bearing assembly on the fixed housing to facilitate superior sealing of the stripper rubber assemblies on the kelly or drilling string during drilling or other well operations. Still another important feature is lubrication of the respective seals and bearings and offsetting well pressure on key shaft pressure seals by introducing the lubricant under pressure into the bearing assembly top pressure seal packing box.
Objects of a rotating blowout preventor in accordance with the Williams '181 patent include a blowout preventor bearing assembly seated on a housing gasket in a fixed housing, a hydraulically-operated clamp mechanism mounted on the fixed housing and engaging the bearing assembly in mounted configuration, which housing is attached to the well casing, wellhead or primary blowout preventor, a vertical inner barrel rotatably mounted in the bearing assembly and receiving a pair of pressure-sealing stripper rubber assemblies and cooling fluid and lubricating inlet ports communicating with top pressure seals for circulating chilled water and/or antifreeze through the top seals and forcing lubricant into stacked shaft bearings and seals to exert internal pressure on the seals and especially, the lower seals.
Specific drawbacks of prior art rotating control head, rotating blowout preventor and/or the like (including a rotating blowout preventor/or rotating control head in accordance with the Williams '181 patent) include, but are not limited to, a.) relying on or using curved clamp segments that at least partially and jointly encircle the housing and bearing assembly; b.) relying on or using clamp segments that are pivotably attached to each other for allowing engagement with and disengagement from the bearing assembly; c.) relying on or using hydraulic clamp(s); d.) relying on or using a mechanical bolt-type connection to back-up a hydraulic clamp for insuring safe operation; e.) poor sealing from environmental contamination at various interface; f.) cumbersome and ineffective stripper rubber assembly attachment; g.) lack or inadequate cooling at key heat sensitive locations of the inner barrel and/or bowl; h.) lack of real-time and/or remotely monitored data acquisition functionality (e.g., via wireless/satellite uploading of data); i.) static (e.g., non-self adjusting) barrel assembly bearing preloading; and j.) cumbersome/ineffective lubrication distribution and cooling.
Therefore, a rotating control head, rotating blowout preventor and/or the like that overcomes abovementioned and other known and yet to be discovered drawbacks associated with prior art oil field drilling equipment (e.g., rotating control head, rotating blowout preventor and/or the like) would be advantageous, desirable and useful.